In connection with the above-referenced type of refiners, in the inner portion of the feed zone the effect of centrifugal force on the supplied material is low. For this reason, the material supplied through the opening in the stationary refining means is generally not fed sufficiently rapidly through the feed zone to the refining zone, which is located radially outward from the feed zone. As a result, the material can clog in the feed zone, which results in friction losses and non-uniform feed, which in turn leads to a deterioration in the pulp quality. In order to overcome these problems, mechanical feeding devices can be arranged in the feed zone.
However, even if the material is transported out through the feed zone by means of central feeding devices, problems can still arise when it enters the refining zone in the refining gap. The material can thus be subjected to braking forces and to an ineffective mechanical action, which causes heat development and results in the material not being adequately worked. This results in unnecessarily high energy consumption.